net.sf.saxon.expr

## Class ErrorExpression

- java.lang.Object
- - net.sf.saxon.expr.Expression
  - - net.sf.saxon.expr.ErrorExpression

- All Implemented Interfaces:
    Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator

      public class ErrorExpression
      extends Expression

  Error expression: this expression is generated when the supplied expression cannot be parsed, and the containing element enables forwards-compatible processing. It defers the generation of an error message until an attempt is made to evaluate the expression
  See Also:
    Serialized Form

- - ### Field Summary

    - ### Fields inherited from class net.sf.saxon.expr.Expression

      `EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, INHERITED_CONTEXT, INSPECTION_CONTEXT, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, NAVIGATION_CONTEXT, NODE_VALUE_CONTEXT, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, W3C_CONSUMING, W3C_FREE_RANGING, W3C_GROUP_CONSUMING, W3C_MOTIONLESS, WATCH_METHOD`

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `ErrorExpression()` This constructor is never executed, but it is used in the expression parser as a dummy so that the Java compiler recognizes parsing methods as always returning a non-null result.
    `ErrorExpression(XPathException exception)` Constructor

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `int` | `computeCardinality()` Determine the static cardinality
    `Expression` | `copy()` Copy an expression.
    `Item` | `evaluateItem(XPathContext context)` Evaluate the expression.
    `void` | `explain(ExpressionPresenter destination)` Diagnostic print of expression structure.
    `XPathException` | `getException()` Get the wrapped exception
    `ExpressionCompiler` | `getExpressionCompiler()` Return the compiler of the Error expression
    `ItemType` | `getItemType(TypeHierarchy th)` Determine the data type of the expression, if possible
    `SequenceIterator` | `iterate(XPathContext context)` Iterate over the expression.
    `Expression` | `optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)` Perform optimisation of an expression and its subexpressions.
    `Expression` | `typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)` Type-check the expression.

    - ### Methods inherited from class net.sf.saxon.expr.Expression

      `addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getExpressionName, getHostLanguage, getImplementationMethod, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getStreamability, getStreamingAdjunct, getSystemId, getSystemId, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, iterateSubExpressionInfo, iterateSubExpressions, markTailFunctionCalls, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toPattern, toStreamingPattern, toString, typeError`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

- - ### Constructor Detail

    - #### ErrorExpression

          public ErrorExpression()

      This constructor is never executed, but it is used in the expression parser as a dummy so that the Java compiler recognizes parsing methods as always returning a non-null result.

    - #### ErrorExpression

          public ErrorExpression(XPathException exception)

      Constructor
      Parameters:
        `exception` - the error to be thrown when this expression is evaluated

  - ### Method Detail

    - #### getException

          public XPathException getException()

      Get the wrapped exception
      Returns:
        the exception to be thrown when the expression is evaluated

    - #### typeCheck

          public Expression typeCheck(ExpressionVisitor visitor,
                             ExpressionVisitor.ContextItemType contextItemType)
                               throws XPathException

      Type-check the expression.
      Overrides:
        `typeCheck` in class `Expression`
      Parameters:
        `visitor` - an expression visitor
        `contextItemType` - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to `Type.ITEM_TYPE`
      Returns:
        the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
      Throws:
        `XPathException` - if an error is discovered during this phase (typically a type error)

    - #### optimize

          public Expression optimize(ExpressionVisitor visitor,
                            ExpressionVisitor.ContextItemType contextItemType)
                              throws XPathException

      Description copied from class: `Expression`
      Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

      This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

      Overrides:
        `optimize` in class `Expression`
      Parameters:
        `visitor` - an expression visitor
        `contextItemType` - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to `Type.ITEM_TYPE`
      Returns:
        the original expression, rewritten if appropriate to optimize execution
      Throws:
        `XPathException` - if an error is discovered during this phase (typically a type error)

    - #### evaluateItem

          public Item evaluateItem(XPathContext context)
                            throws XPathException

      Evaluate the expression. This always throws the exception registered when the expression was first parsed.
      Overrides:
        `evaluateItem` in class `Expression`
      Parameters:
        `context` - The context in which the expression is to be evaluated
      Returns:
        the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
      Throws:
        `XPathException` - if any dynamic error occurs evaluating the expression

    - #### iterate

          public SequenceIterator iterate(XPathContext context)
                                   throws XPathException

      Iterate over the expression. This always throws the exception registered when the expression was first parsed.
      Overrides:
        `iterate` in class `Expression`
      Parameters:
        `context` - supplies the context for evaluation
      Returns:
        a SequenceIterator that can be used to iterate over the result of the expression
      Throws:
        `XPathException` - if any dynamic error occurs evaluating the expression

    - #### getItemType

          public ItemType getItemType(TypeHierarchy th)

      Determine the data type of the expression, if possible
      Specified by:
        `getItemType` in class `Expression`
      Parameters:
        `th` - the type hierarchy cache
      Returns:
        Type.ITEM (meaning not known in advance)

    - #### computeCardinality

          public int computeCardinality()

      Determine the static cardinality
      Specified by:
        `computeCardinality` in class `Expression`
      Returns:
        the computed cardinality, as one of the values `StaticProperty.ALLOWS_ZERO_OR_ONE`, `StaticProperty.EXACTLY_ONE`, `StaticProperty.ALLOWS_ONE_OR_MORE`, `StaticProperty.ALLOWS_ZERO_OR_MORE`

    - #### copy

          public Expression copy()

      Copy an expression. This makes a deep copy.
      Specified by:
        `copy` in class `Expression`
      Returns:
        the copy of the original expression

    - #### getExpressionCompiler

          public ExpressionCompiler getExpressionCompiler()

      Return the compiler of the Error expression
      Overrides:
        `getExpressionCompiler` in class `Expression`
      Returns:
        the relevant ExpressionCompiler

    - #### explain

          public void explain(ExpressionPresenter destination)

      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
        `explain` in class `Expression`
      Parameters:
        `destination` - the expression presenter used to display the structure

Copyright (c) 2004-2013 Saxonica Limited. All rights reserved.